This invention relates in general to pressure sensors and in particular to a pressure sensor which is integrated into an electro-hydraulic control unit for an antilock brake system.
An anti-lock brake system (ABS) is often included as standard equipment on new vehicles. When actuated, the ABS is operative to control the operation of some or all of the vehicle wheel brakes. A typical ABS, which controls all four vehicle wheels, includes a plurality of normally open and normally closed solenoid valves which are mounted within a control valve body and connected to the vehicle hydraulic brake system. A separate hydraulic source, such as a motor driven pump, is included in the ABS for reapplying hydraulic pressure to the controlled wheel brakes during an ABS braking cycle. The pump is typically included within the control valve body while the pump motor is mounted upon the exterior of the control valve body.
It is also known to provide an ABS for the rear wheels only. Such a system is commonly referred to as a rear wheel anti-lock brake system (RWAL). Typically, RWAL does not include a motor driver pump, but utilizes the vehicle master brake cylinder as a source of pressurized brake fluid. While RWAL has a limited volume of pressurized brake fluid available during an ABS braking cycle, elimination of the pump and pump motor simplifies the system while reducing the cost thereof.
Both four wheel ABS and two wheel RWAL include an electronic control module which has a microprocessor. The control module is electrically coupled to the pump motor, for a four wheel ABS. The control module also is connected to a plurality of solenoid coils associated with the solenoid valves and one or more wheel speed sensors for monitoring the speed and deceleration of the controlled wheels. The control module also is electrically coupled to a pressure sensor which monitors the pressure generated by the vehicle master cylinder. The control module is typically mounted within a removable housing which is attached to the control valve body to form a compact unit which is often referred to as an ABS Electro-hydraulic Control Unit (ECU).
It is known to mount the coils for actuating the solenoid coils within the control module housing. Tubular sleeves which enclose the valve armatures extend from the valve body, forming a seal for the hydraulic brake circuit. When the control module housing is mounted upon the valve body, each of sleeves is received by an associated solenoid coil. Accordingly, the housing can be removed from the valve body for servicing of the control module electronics without opening the hydraulic brake circuit.
During vehicle operation, the microprocessor in the ABS control module continuously receives speed signals from the wheel speed sensors and pressure signals from the pressure sensor. The microprocessor monitors the wheel speed signals and pressure signals for potential wheel lock-up conditions. When the vehicle brakes are applied and the microprocessor senses an impending wheel lock-up condition, the microprocessor is operative to actuate the pump motor, in a four wheel ABS. The microprocessor also is operable to selectively operate the solenoid valves in the valve body to cyclically relieve and reapply hydraulic pressure to the controlled wheel brakes. The hydraulic pressure applied to the controlled wheel brakes is adjusted by the operation of the solenoid valves to limit wheel slippage to a safe level while continuing to produce adequate brake torque to decelerate the vehicle as desired by the driver.
This invention relates to an improved pressure sensor which is integrated into an electro-hydraulic control unit for an anti-lock brake system.
Typically, prior art pressure sensors used in Anti-lock Brake Systems (ABS) are threaded into either a port in the vehicle master cylinder or an external surface of the electro-hydraulic control valve. The external pressure sensor location exposes the sensor to the under-hood operating environment of the vehicle and requires that the sensor be hermetically sealed. Installing a threaded pressure sensor is labor intensive and has a potential for introducing contaminants into the brake fluid. Such pressure sensors also require a dedicated wiring harness which requires an additional manufacturing process step of connecting the harness end to the sensor. Accordingly, it would be desirable to provide an alternate sensor design which eliminates these difficulties.
The present invention contemplates a hydraulic control unit for a vehicle brake system that includes a valve body that is adapted to be connected to the vehicle brake system. The valve body carrying at least one solenoid valve and has a bore formed therein that communicates with hydraulic brake fluid. A pressure sensor is mounted in the valve body bore. A removable housing that encloses the pressure sensor is attached to the said valve body. The housing also carries a circuit substrate that has electrical traces disposed thereon. An electrical connector is mounted upon the circuit substrate and cooperates with the pressure sensor when the housing is mounted upon the valve body to form an electrical connection between the electrical traces disposed upon the circuit substrate and the pressure sensor. The electrical connection being enclosed by the housing and the valve body.
In the preferred embodiment, the pressure sensor includes a body having a first portion that is received by the valve body bore. The first portion of the pressure sensor carries a resilient seal that forms a seal with the valve body. Additionally, the valve body bore includes a threaded surface and the first portion of the pressure sensor body also includes a threaded surface that cooperates with the bore threaded surface to retain said pressure sensor in said valve body bore.
It is also contemplated that the pressure sensor includes an electrical connector mounted upon an end thereof. The pressure sensor electrical connector cooperates with the electrical connector mounted upon said circuit substrate to form an electrical connection between electrical traces disposed upon the circuit substrate and the pressure sensor.
It is further contemplated that a first member of a pump motor electrical connector is mounted upon the circuit substrate and a second member of the motor electrical connector is carried by the valve body. The first and second members of the motor connector cooperate when the housing is mounted upon the valve body to form an electrical connection between electrical traces disposed upon the circuit substrate and a pump motor. As with the pressure sensor connector, the pump motor electrical connection is enclosed by the housing and the valve body.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.